The invention relates to an adaptive picture delay for use in motion-compensated processing operations, like a motion vector estimation, motion vector compensated interpolation or a motion-compensated noise reduction.
European Pat. Application No. EP-A-0,514,012, corresponding to U.S. Pat. 5,428,399, discloses a method and apparatus for a standard conversion of an image signal. Images may be stored on film or on one of the TV/video standards. Movie film comprises a sequence of frames at a 24 Hz rate, each film frame representing a certain movement phase. Video, however, comprises a sequence of interlaced fields at a 50 Hz or 60 Hz rate, each field representing a certain movement phase. Due to these inherent differences, when converting from film to one of the TV standards, or between the TV standards when at least part of the image originates from film, distortions are introduced, particularly when there are any objects moving in the image.
Images recorded on film are stored at 24 frames per second. Such images, if replayed at a slightly higher rate, namely, 25 frames per second, can readily be used for the PAL standard which uses 50 interlaced fields per second, whereby each film frame is repeated to form two video fields.
The conversion process is more complicated when the images are initially stored on film at a frame rate of 24 frames per second and it is desired to convert these images to the NTSC standard at 60 interlaced fields per second, because of the non-integral relationship of 60 to 24. In general, 5 video fields are made from 2 film frames by taking 3 consecutive video fields from 1 film frame, and 2 consecutive video fields from the next film frame. This is usually known as 3-2 pull-down conversion.
So as to accommodate for moving objects, a motion vector estimator provides motion vectors which are indicative of any objects moving and are used to manipulate the standards converter. The greatest errors have been encountered when transferring images previously subjected to a 3-2 pull-down conversion to obtain an NTSC signal, to the PAL standard. To cope with this problem, European Patent Application EP-A-0,514,012 discloses a technique in which each field of the output video signal has contributions from 4 input fields. Since the motion estimator can detect the phase of the 3-2 pull-down conversion, the correct input fields contribute to each output field. In a preferred embodiment of the prior art, 4 field stores are used. Alternatively, there may be only 2 field memories which is actually simpler to implement, but the conversion does not have the same performance of brightness changes and vector inaccuracies. An optimum compromise between the standards converter becoming too complex and adequate resolution on translating images, has been found when there are 4 fields stored at any one time in the standards converter.
It is, inter alia, an object of the invention to provide a memory control which enables a reduction in required memory capacity without a visible reduction in quality. To this end, a first aspect of the invention provides an image information storing method. A second aspect of the invention provides an image information storing arrangement incorporating the method. A third aspect of the invention provides an image processing apparatus comprising such an image information storing arrangement.
In accordance with the present invention, image information is stored into a memory device which is controlled in such a manner that only image information from a movement phase different from the movement phase of the image information already stored in the memory device, is stored into the memory device, whereby the memory device provides image information from a movement phase which differs from a movement phase of the image information by a fixed number of movement phases, even when the image information contains repeated movement phases, e.g., when the image information originates from movie film. The invention is preferably applied in an image processing apparatus, like a television set, a digital video disk (DVD) player, or a PC equipped for processing images.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.